Planificación de la accesibilidad urbana basada en índices jerárquicos analíticos

La accesibilidad urbana está relacionada con la posibilidad de conseguir bienes y servicios, realizar actividades y alcanzar destinos. El fin último de la gran parte de los desplazamientos en las ciudades es el acceso. La medida de la accesibilidad suele basarse en cuestiones de tiempo, coste, comodidad y riesgo necesarios para llegar a las oportunidades que ofrece la ciudad. Medir la accesibilidad globalmente es una tarea compleja puesto que en ella influye una gran cantidad de factores, pero imprescindible en cualquier proceso de planificación orientado a la mejora de la movilidad. En los últimos años se vienen utilizando algunos indicadores relacionados con la movilidad. En muchos casos estos índices sólo reflejan una perspectiva parcial en la planificación. Un alternativa es definir índices globales que ponderen los factores relevantes de acuerdo con los objetivos perseguidos. En este contexto, el análisis multicriterio basado en procesos jerárquicos analíticos es una herramienta muy útil para eliminar en lo posible la subjetividad inherente a la asignación de prioridades en la ponderación. Además, la utilización de los Sistemas de Información Geográfica puede ayudar en la representación espacial de este análisis, aportando información alfanumérica a los elementos gráficos que definen el modelo. Se propone un “índice de accesibilidad sostenible” que permitirá cuantificar la accesibilidad urbana. Esto hará posible diagnosticar los problemas esenciales de movilidad, proponer soluciones adecuadas y evaluar la eficacia de las medidas adoptadas. Todo ello constituirá un proceso dinámico encaminado a la mejora sostenible de la calidad de vida en las ciudades

Active Learning and Dynamic Pricing Policies

In this paper, we address the problem of dynamic pricing to optimize the revenue coming from the sales of a limited inventory in a finite time-horizon. A priori, the demand is assumed to be unknown. The seller must learn on the fly. We first deal with the simplest case, involving only one class of product for sale. Furthermore the general situation is considered with a finite number of product classes for sale. In particular, a case in point is the sale of tickets for events related to culture and leisure; in this case, typically the tickets are sold months before the event, thus, uncertainty over actual demand levels is a very a common occurrence. We propose a heuristic strategy of adaptive dynamic pricing, based on experience gained from the past, taking into account, for each time period, the available inventory, the time remaining to reach the horizon, and the profit made in previous periods. In the computational simulations performed, the demand is updated dynamically based on the prices being offered, as well as on the remaining time and inventory. The simulations show a significant profit over the fixed-price strategy, confirming the practical usefulness of the proposed strategy. We develop a tool allowing us to test different dynamic pricing strategies designed to fit market conditions and seller s objectives, which will facilitate data analysis and decision-making in the face of the problem of dynamic pricing

Agent-based model for the effect of curing temperature on cement hydration

The agent-based model presented here, comprises an algorithm that computes the degree of hydration, the water consumption and the layer thickness of C-S-H gel as functions of time for different temperatures and different w/c ratios. The results are in agreement with reported experimental studies, demonstrating the applicability of the model. As the available experimental results regarding elevated curing temperature are scarce, the model could be recalibrated in the future. Combining the agent-based computational model with TGA analysis, a semiempirical method is achieved to be used for better understanding the microstructure development in ordinary cement pastes and to predict the influence of temperature on the hydration process

Nanoscale Agent Based Modelling for Nanostructure Development of Cement

Most of macroscopic properties of materials are consequences of processes taking place at the nanoscale. Investigation of phenomena at the sub-micro level to improve the performance of construction materials is one of the main applications of Nanotechnology in Construction. The modelling and simulation of nanostructures is then essential to provide a better understanding of the behaviour of construction materials. We present in this paper an agent-based modelling approach in which a set of interacting agents, capable of organizing themselves dynamically and of adapting to the environment, encapsulate the behaviour of the whole system. This new approach is used for studying the nanostructure development of cement, considering that each individual particle develops its own C-S-H shell critical thickness which triggers the agent for shifting the algorithm to next stage. The algorithm results were compared and found in good agreement with reported experimental work

Agent-based modelling for cement hydration

The Agent-Based Modelling and simulation (ABM) is a rather new approach for studying complex systems withinteracting autonomous agents that has lately undergone great growth in various fields such as biology, physics, social science, economics and business. Efforts to model and simulate the highly complex cement hydration process have been made over the past 40 years, with the aim of predicting the performance of concrete and designing innovative and enhanced cementitious materials. The ABM presented here - based on previous work - focuses on the early stages of cement hydration by modelling the physical-chemical processes at the particle level. The model considers the cement hydration process as a time and 3D space system, involving multiple diffusing and reacting species of spherical particles. Chemical reactions are simulated by adaptively selecting discrete stochastic simulation for the appropriate reaction, whenever that is necessary. Interactions between particles are also considered. The model has been inspired by reported cellular automata?s approach which provides detailed predictions of cement microstructure at the expense of significant computational difficulty. The ABM approach herein seeks to bring about an optimal balance between accuracy and computational efficiency

Modelling hydration process of cement nanoparticles by using an agent-based molecular formation algorithm.

This paper presents an agent-based modelling approach for hydration process of Portland cement taking place at the nanoscale. By following a combination of stochastic, deterministic and adaptive rules, cement system is allowed to evolve from an anhydrous separated state to a bond state with enhanced mechanical properties. We consider the two main chemical reactions producing C-HS gel and portlandite, and identify the related anhydrous cement components as two autonomous agents, while water and hydration time are viewed as activator agents. The material representation consists of a geometrical configuration based on a two-dimensional granular fluid, which shows to be suitable when studying nanostructure formation. The resulting agent-based model is tested on a 103μm x 103μm thin film with 20μm thickness containing anhydrous cement. We evaluate the modelling approach after 7 days of hydration from comparison with experimental results, and agreement is good

Multidisciplinary Learning, Another way of Teaching Maths in Engineering

Multidisciplinary training is widely appreciated in industry and business, and nevertheless usually is not addressed in the early stages of most undergraduate programs. We outline here a multidisciplinary course for undergraduates studying engineering in which mathematics would be the common language, the transverse tool. The goal is motivating students to learn more mathematics and as a result, improve the quality of engineering education. The course would be structured around projects in four branches in engineering: mechanical, electrical, civil and bio-tech. The projects would be chosen among a wide variety of topics in engineering practice selected with the guidance of professional engineers. In these projects mathematics should interact with at least two other basic areas of knowledge in engineering: chemistry, computers science, economics, design or physics

Relationships between agents for modelling the intermediate stages of cement hydration

Agent-Based modelling is, in many cases, most natural for describing and simulating a system composed of “behavioral” entities. Whether one is attempting to describe the complex process of cement hydration, an agent-based approach makes the model seem closer to reality. Therefore, it is more natural to describe how the calcium silicate phases individually behave during the hydration Chemistry than to come up with the equations that govern the dynamics of the anhydrous constituents. Because the dynamic equations result from the behavior of the calcium silicate phases, the agent-based model will also enable to study aggregate properties. A model based on agents for the cement hydration, also makes it possible to analyse the formation and growing of the C-S-H gel: the main binding agent in hardened cement. Knowing the initial concentration of the anhydrous constituents makes it possible to create virtual agents which represent and behave according with their reactivity. This work describes an algorithm which cores an agentbased approach for modelling the intermediate stages of cement hydration, focusing on the microstructure development and C-S-H gel formation. Theories relating to the mechanism of cement hydration are examined and these are discussed in terms of the agents behavioral. Monte Carlo method is applied to obtain and analyse the algorithm result

Implicit equations of non-degenerate rational Bezier quadric triangles

In this paper we review the derivation of implicit equations for non-degenerate quadric patches in rational Bézier triangular form. These are the case of Steiner surfaces of degree two. We derive the bilinear forms for such quadrics in a coordinate-free fashion in terms of their control net and their list of weights in a suitable form. Our construction relies on projective geometry and is grounded on the pencil of quadrics circumscribed to a tetrahedron formed by vertices of the control net and an additional point which is required for the Steiner surface to be a non-degenerate quadric

Estructuras de hormigón armado bajo carga dinámica severa. Parte III: ejemplo de simulación numérica

Publicamos la tercera parte y última de este artículo sobre estructuras de hormigón armado bajo carga dinámica severa en el que, los autores, nos han ido exponiendo diferentes ejemplos. En esta ocasión, se pone patente que con el desarrollo de los ordenadores durante las últimas décadas se ha dado la posibilidad de utilizar el método de los elementos finitos (FEM: Finite Elements Method) para estudiar los efectos de una carga dinámica severa, como en el caso de las explosiones. A continuación se describe el uso del método para este tipo de situaciones de carga